The present invention relates to a fastener and a method for attaching metal members therewith for assembling automotive vehicle structures.
It is known that the manufacture of automotive vehicles often requires that metal members be attached to each other for forming automotive vehicle structures. Friction stir welding is one potential method of attaching metal members. Conventional friction stir welding typically requires a rotating tool to be translated along an interface between surfaces of metal members for softening or melting portions of the members at the interface. In turn, the softened or melted portions intermix and harden to form metallurgical bonds between the members. During a conventional friction stir welding process, however, amounts of liquidized material may be lost or unused. Moreover, it may be difficult to conventionally friction stir weld relatively thick members, since thicker members tend to dissipate heat relatively quickly thereby frustrating desired intermixing of liquidized material for forming metallurgical bonds. Thus, there is a need for improved techniques, fasteners or both, alternative to conventional friction stir welding for achieving high integrity attachment of metal members.
The present invention meets these needs by providing an improved fastener for attaching metal members and an improved method for attaching metal members with the fastener. The fastener and method find particular utility in the formation of components for an automotive vehicle.
According to the method, a first metal member is provided and contacted with a second metal member. A metal fastener is also provided. The fastener is substantially symmetrical about a central axis and includes a radially enlarged cap portion and a shank portion extending from the cap portion. The fastener also includes a core with a cladding covering at least a portion of an outer peripheral surface of the core wherein the cladding is metallurgically bonded with the core. Once provided, the metal fastener is rotated about the axis using a rotary driving apparatus and the fastener is driven through the first member and into the second member during rotation. In turn, friction is induced between the fastener, the first member and the second member for at least locally melting portions of the cladding, the first member and the second member to form a flowable material about the fastener. Preferably, the melted portions of the cladding alloy with the melted portions of the first and second members to metallurgically bond the first and second metal members to the fastener. The flowable material is solidified to integrally attach the flowable material to the first member and second member with a metallurgical bond.
The fastener is adapted to be driven through a sheet and into a substrate. Accordingly, the fastener includes a core with an outer peripheral surface, the core being formed of a refractory metal with a melting point higher than the sheet or the substrate. The fastener also includes a cladding disposed upon a substantial portion of the outer peripheral surface, the cladding being a metal alloy. Additionally, the fastener has a substantially disk-shaped cap portion with a non-circular cavity disposed therein and has a substantially cylindrical shank portion with a leading surface. Preferably, the fastener is substantially symmetrical about a central axis.